The invention relates generally to a copier and copying method.
More particularly, the invention relates to a photographic copier and a method of copying photographic masters. The copier has a device for masking the masters and a device for measuring the densities of the masters. A logic circuit utilizes the data from the measuring device to determine whether masking is required and, if so, the degree of masking.
Copies of photographs having large intensity variations in localized regions are often overexposed in the light areas and underexposed in the dark areas. As a result, details or fine structures are poorly reproduced, or not reproduced at all, on the paper image.
The German Offenlegungsschrift 31 41 263 discloses a method of copying color diapositives on reversal paper using masks to reduce contrast. The diapositive is placed in direct contact with phototropic glass which is then illuminated via the diapositive by means of an ultraviolet lamp or the like. A negative black-and-white mask of the diapositive is thereby produced in the phototropic glass. The composite of mask and diapositive is held in position and illuminated from the other direction to thus form an image of the diapositive on the reversal paper with low contrast. The Offenlegungsschrift describes how the method may be applied to a photographic copier for a large laboratory. To this end, a rotating endless band is provided and is equipped with elements of phototropic glass. After each copying operation, the band is advanced in such a manner that the next glass element is located in the path of the copy light.
Another photographic copier suitable for masking is disclosed in the German patent 28 20 965. Here, the mask is produced on an LCD matrix which is controlled by an electronic regulating circuit and is disposed between the illuminating system and the master.
In principle, both of the masking procedures outlined above can be applied in modern copiers of high capacity. However, it is then absolutely necessary for the copiers to be equipped with a logic circuit which decides whether a master should be masked and, if yes, to what degree. It has now been found that this is very difficult to achieve. For a better understanding as to why, two examples are briefly described below.
If an object or a person is photographed against the light, the object or person is black on a conventional copy while the background is normally illuminated or the background is greatly overexposed with contours of the object or person being detectable. For such photographs, the contrast between foreground and background can be sharply reduced by masking so that the contours of the foreground are visible even when the background is normally illuminated. The situation is entirely different when a photograph shows a black cat sitting in the snow. A logic circuit making a decision about masking based on the large-area contrast would mask this photograph also during the copying operation. The result would be a largely false reproduction. The white snow would certainly be somewhat dark while the black cat would be lighter and brownish. Such a reproduction is unsatisfactory to a photographer.